How would you go about finding a formula for diminishing returns that matches this (wasnt sure on the tag either, apologies if it does not fit but it wasnt a linear equation that I could figure out so it might be differential?):
4.0 1
3.7 2
3.5 3
3.16 4
2.9 5
2.74 6
2.56 7
2.4 8
2.255 9
2.12 10
2 11
1.88 12
1.786 13
1.692 14
1.6 15
1.52 16
1.45 17
1.38 18
1.31 19
1.257 20